Patent GB-1091367-A (GB)
Title: Heterofilaments
Inventor: BRAYFORD JOHN RAYMOND
IPC: D01D5/32
Filed: 1965-06-23
Abstract: 1,091,367. Spinneret for conjugate filaments. IMPERIAL CHEMICAL INDUSTRIES Ltd. June 17, 1966 [June 23, 1965], No. 26598/65. Heading B5B. A spinneret comprises a spinneret plate bearing a multiplicity of spinneret holes substantially perpendicularly disposed to the face of the spinneret plate, one portion of the wall of each of the said spinneret holes extending substantially further at the exit than one other portion of the wall of each of said spinneret holes. The extended portion of the wall may be of uniform length, or the exit of the spinneret holes may be bevelled. In Figs. 1 and 2, a spinneret is fabricated from a spinneret plate of circular form in which are bored 12 equidistant spinneret holes, the axes of which are perpendicular to the face of the spinneret plate and the centres of which are on a circle concentric therewith. From the outer face of the spinneret plate is machine a circular groove, shown in cross section through a diameter at A, B, C, D in Fig. 2 or A<1>, B<1>, C<1>, D<1> in Fig. 3 of such dimensions that each of the spinneret holes is modified so that the length of the wall of the straight portion F, D of the spinneret hole at the point nearest to the axis G, H, of the spinneret plate is 0À050 inch, the length of the wall E, C at the point farthest from the axis of the spinneret plate is 0À030 inch and wall lengths between these two points are intermediate in a smooth gradation. In addition to the step pattern (Fig. 6), the spinneret hole may alternatively be of the bevel pattern (Fig. 5) or sharp edge bevel pattern (Fig. 4). In the case of a stepped exit to the spinneret hole it is not necessary that the interface between the two polymer streams should coincide with the line of occurrence o the step differential but the two polymer com ponents should each be uniformly distributed above the line at right angles to the line of occurrence of the step differential. In the term spinneret hole is included only the substantially parallel sided portion of the orifice through which the molten polymer is forced, excluding any lead-in portion of wider bore than the parallel-sided portion, which has a negligible effect on the velocity of the polymer stream. Such spinnerets are useful for the manufacture of conjugate filaments by forcing a stream of molten polymer of higher viscosity side by side with a stream of molten polymer of lower viscosity through a spinneret hole, the wall length of which is non-uniform, the major part or all of the polymer of lower viscosity being in contact with the major part or all of a set portion of the wall of the spinneret hole extending further than the remainder of the wall of the spinneret hole at the exit so as to counteract substantially the tendency to deflection of the polymer stream resulting from the difference in melt viscosity between the two polymer streams. In a preferred method, the molten polymer of higher viscosity has a viscosity at the spinning temperature of from 1000- 10,000 poises, especially 1,700-3,000 poises, the viscosity of the lower viscosity polymer is of at least 500 poises less, desirably at least 1,500 poises less than the viscosity of the higher viscosity polymer, the ratio in which the two components are forced through the spinneret is from 1: 5 to 5: 4, especially 1: 3 to 3: 1, the hole diameter is not less than 0À007, preferably not less than 0À009, and not greater than 0À020 inch, and especially not greater than 0À015 inch, the hole length is not less than 0À01, preferably not less than 0À02, and not greater than 0À05 inch, the difference between the greatest and shortest lengths of the spinneret walls is not less than 0À002 and not greater than 0À020 inch, preferably not less than 0À004 and not greater than 0À010 inch and the throughput of the combined stream of polymer is from 0À5 g. to 2À5 g. per min. per hole. The pairs of polymers used must differ significantly in melt viscosity, the difference in the melt viscosities between the two polymers under the conditions of shear and temperature pertaining within the spinneret orifice being sufficient so that the velocity distribution across the conjugate stream issuing from the spinneret hole is significantly asymmetrical. Polymers which fulfil this requirement are those of which the flow behaviour is predominantly Newtonian or pseudoplastic, e.g. polyesters and polyamides. Polymers which may not fill this requirement are those of which the melt is predominantly visco-elastic, e.g. fibre forming polyolefines. The pairs of polymers of different melt viscosity may be of different chemical composition, e.g. polyester with polyamide, of modified chemical composition, e.g. polyester with copolyester, or of different molecular weights for the same polymer. Otherwise the difference in melt viscosity may be produced by some other means, e.g. a difference in temperature or the use of particular polymer paired with the same polymer in an admixture with a modifying agent; an example of such a modifying agent is a finely divided chemically inert material. The spinning of conjugate filaments derived from two polyethylene terephthalate melts differing in melt viscosity by a factor of approximately 4 to 1 due to molecular weight difference is described.